Avermectin compounds are known antiparasitic agents of considerable activity. The preparation of the natural material products, the 22, 23 dihydro derivatives and the monosaccharide and aglycone derivatives are known and described in U.S. Pat. Nos. 4,320,519, 4,199,569 and 4,206,205, respectively. The preparation of hydroxylated avermectin aglycones is also known. In particular, U.S. Pat. No. 4,666,937 describes a process for producing 27-hydroxy avermectin aglycone derivatives which employs the microorganism Cunninghamella blakesleeana and produces low yields of only one stereoisomer of the 27-hydroxy compounds. Additionally, U.S. Pat. No. 5,140,042 describes the biotransformation process of producing 28-hydroxy derivatives of ivermectin aglycone using Saccharopolyspora (S.) erythrea. The hydroxylation at C28 with S. erythrea occurs with ivermectin aglycone as the substrate and not with avermectin B1 a aglycone. The instant process is significantly different in that S. erythrea is used to hydroxylate both ivermectin aglycone and avermectin aglycone at the C27 position and yields both stereoisomers (designated A and B isomers) with either compound. Additionally, both 27-OH avermectin aglycone isomers are derivatized to dissacharides and then further glycosylated to yield novel 4"-O-glucosyl 27-OH compounds.